Bloom et al. in U.S. Pat. No. 5,311,360, entitled “Method and Apparatus for Modulating a Light Beam,” teach a grating light valve™ light modulator which operates in a reflection mode and a diffraction mode. The grating light valve™ light modulator type device includes elongated elements suspended above a substrate. In the reflective mode, reflective surfaces of the grating light valve™ light modulator type device cause incident light to constructively combine to form reflected light. In the diffractive mode, the reflective surfaces of the grating light valve™ light modulator type device are separated by a quarter wavelength of the incident light to produce diffracted light. When the grating light valve™ light modulator type device is in the diffractive mode, the grating light valve™ light modulator type device predominantly diffracts light into a plus one diffraction order and a minus one diffraction order but also diffracts a small amount of light into higher diffraction orders.
Bloom et al. further teach an alternative grating light valve™ light modulator type device in which the elongated elements include off-axis neck portions at ends of each of the elongated elements. In a non-activated mode, the elongated elements are parallel causing incident light to reflect from the elongated elements and, thus, produce the reflected light. In an activated mode, each of the elongated elements is rotated about an axis defined by the off-axis neck portions to diffract light in a similar manner as a sawtooth grating.
Because the light modulator is switched between the non-activated mode and the activated mode and because the non-activated mode diffracts small quantities of light into the same angles as does the activated mode, a contrast between the non-activated state and the activated state is less than an optimum contrast.
The co-owned, co-filed, and co-pending U.S. patent application, Ser. No. 09/930,838, entitled BLAZED GRATING LIGHT VALVE teach a diffractive light modulator, which operates in a reflection mode and a diffraction mode. The diffractive light modulator includes elongated elements arranged in groups. The elongated elements within each group are progressively stepped downward. The groups of elements lic in a plane parallel to a substrate. The co-owned, co-filed, and co-pending U.S. patent application Ser. No. 09/930,838, entitled BLAZED GRATING LIGHT VALVE is hereby incorporated by reference.
Light directed into plus or minus first orders, or higher orders, can be collected as different outputs of an optical switch. However, since light modulators diffract small portions of light into angles other than an intended primary diffraction angle, this can lead to crosstalk, which is interference from adjacent channels. What is needed is a light modulator that minimizes crosstalk in switching applications.